I had read somewhere in the last few weeks that the G6 sensor code is like the old calibration codes that were associated with a vial of test strips. It was a way to calibrate the meter with a batch of test strips. The post I read noted that s/he had one code common to two if the three sensors in the three sensor box.
This sensor code was talked about a lot in relationship with the pre-release speculation as to how Dexcom would deter restarts. When people started to point out that codes were often duplicated, that argued against the sensor code number being part of the re-start deterrence design.